Die Farbe des Himmels: II     

F. Möller  E. de Bary  G. Krog 《Pure and Applied Geophysics》1953,26(1):141-152

Zusammenfassung Unter Verwendung der in einer früheren Untersuchung(1) mitgeteilten Formeln werden Farbton, Sättigung und Leuchtdichte des gesamten Himmels unter exakter Berechnung der sekundären Streuung in einer dunstgetrübten Atmosphäre bestimmt. Es zeigt sich dabei, dass der vonWiener undBernhardt gemachte Versuch, die Vielfachstreuung durch Einsetzen und Summieren einer geometrischen Reihe für primäre, sekundäre usw. Streuung zu approximieren, fehlerhafte Ergebnisse liefern muss, weil das Verhältnis sekundär: primär stellenweise>1 wird. In dem durch die Sonne gehenden Horizontalkreis bleiben Farbton und Sättigung konstant und nur die Leuchtdichte ändert sich in den Fällen, dass lediglich die molekulare Streuung (ungetrübte Atmosphäre) oder lediglich die Dunststreuung (grosse Trübung, nahe der Sonne) wirksam ist.—Der Einfluss einer geänderten Grössenverteilung des Aerosols wird untersucht.

---

Summary Using formulas given in a former investigation (1), we computed the colour, saturation and brightness of the whole sky. With this, the secondary scattering of a turbid atmosphere was exactly determined. It is shown that wrong values will result by use ofWiener's method of approximating the multiple scattering by a geometrical series of primary, secondary a.s.o. scattering, because at some parts of the sky the proportion of secondary: primary is >1. In the horizontal circle through the sun, colour shade and saturation are constant and only the brightness varies, if either only molecular scattering (unturbid atmosphere) or only haze scattering (strong turbidity, small distance from the sun) dominates. Further, the influence of variations of the seize distribution of the aerosol is investigated.

---

Résumé En utilisant les formules communiquées dans une publication antérieure (1) la couleur, la saturation et la luminosité du ciel entier sont calculés en tenant compte de la réfraction secondaire dans une atmosphère brumeuse. On constate que l'essai deWiener etBernhardt d'approcher la réfraction multiple par une progression géométrique pour la réfraction primaire, secondaire etc. doit mener à des faux résultats parce que la proportion de secondaire: primaire devient en partie >1. Dans le plan horizontal passant par le soleil, la couleur et la saturation restent de même; seulement la luminosité change dans le cas ou seul la réfraction moléculaire (atmosphère non troublée) ou seul la réfraction brumeuse (beaucoup de brume, tout près du soleil) sont efficaces. L'influence d'une autre répartition de grandeur de l'aérosole est examinée.

  相似文献   

Verification of multispecies interactions in the North Sea by trawl survey data on Norway pout (Trisopterus esmarkii)     

Sparholt  Henrik; Larsen  Lena I.; Nielsen  J.Rasmus 《ICES Journal of Marine Science》2002,59(6):1270-1275

  相似文献   

Pollutant—particle associations and dynamics in coastal marine environments: a review     

C. R. Olsen  N. H. Cutshall  I. L. Larsen 《Marine Chemistry》1982,11(6):501-533

A wide variety of substances, including known or potential pollutants, become associated with particles in coastal marine environments. This association may result from: (1) ion exchange, precipitation, or hydrophobic interactions with the particle surface, (2) co-precipitation with iron and manganese hydrous oxide coatings, (3) complexation with organic substances bound or aggregated with particles, (4) incorporation into mineral lattices, organisms or fecal material, or (5) flocculation of colloidal organic and inorganic matter during river and sea water mixing. The transport, accumulation and fate of such chemically-reactive pollutants in coastal marine environments are governed to a great extent by particle dynamics. Understanding of the mechanisms and processes affecting pollutant-particle associations and dynamics allows the prediction of the fate of a wide variety of pollutants in estuarine, coastal and marine environments.  相似文献   

Frequency of sediment movement on the Washington continental shelf: A note     

Richard W. Sternberg  L.H. Larsen 《Marine Geology》1976,21(3):M37-M47

Several independent sets of field data have been analyzed in order to estimate the frequency of sediment movement on the continental shelf off Washington over an annual period and to identify the major components of the bottom velocity field causing this motion. Sediment motions resulting from: (1) bottom currents caused by surface wind stress and tides, and (2) wave-induced oscillatory bottom currents have been investigated. Analysis of a 260-day current record from 3 m off the seabed at 80 m depth on the continental shelf and a 205-day open-ocean wave record collected on Cobb Seamount 465 km west of the Washington coast suggest that the threshold of sediment motion was exceeded for approximately 22 days per year as a result of mean currents (20 min time averaged) and approximately 53 days per year from wave-induced oscillatory currents. Substantial variations can be expected from year to year, so these values represent order of magnitude estimates.  相似文献   

A dated volcano-tectonic deformation event in Jan Mayen causing landlocking of Arctic charr     

Eiliv Larsen  Astrid Lyså  Ármann Höskuldsson  Jan G. Davidsen  Marie J. Nadeau  Michael Power  Georgios Tassis  Stefan Wastegård 《第四纪科学杂志》2021,36(2):180-190

We provide the first documentation of tectonic deformation resulting from a volcanic eruption on the island of Jan Mayen. Vertical displacement of about 14 m southwest of the stratovolcano Beerenberg is associated with an eruption in ad 1732 on its southeastern flank. The age of the uplift event is bracketed by radiocarbon-dated driftwood buried by material deposited due to uplift, and by tephra from this eruption. Constraints, inferred from radiocarbon ages alone, allow for the possibility that uplift was completed prior to the ad 1732 eruption. However, the occurrence of tephra in the sediment column indicates that some displacement was ongoing during the eruption but ceased before the eruption terminated. We attribute the tectonic deformation to intrusion of shallow magma associated with the volcanic eruption. Our results complement previous studies of volcanic activity on Jan Mayan by providing precise age constraints for past volcanic activity. Also, it raises new hypotheses regarding the nature, timing and prevalence of precursor tectonic events to Jan Mayan eruptions. The uplift caused the complete isolation of a coastal lake by closing its outlet to the sea, thus landlocking the facultative migratory fish species Arctic charr (Salvelinus alpinus).  相似文献   

The influence of relative sediment supply on riverine habitat heterogeneity   总被引：1，自引：0，他引：1  

Sarah M. Yarnell  Jeffrey F. Mount  Eric W. Larsen 《Geomorphology》2006,80(3-4):310-324

The diversity of aquatic habitats in streams is linked to physical processes that act at various spatial and temporal scales. Two components of many that contribute to creating habitat heterogeneity in streams are the interaction between sediment supply and transport capacity and the presence of local in-stream structures, such as large woody debris and boulders. Data from previously published flume and field studies and a new field study on tributaries to the South Yuba River in Nevada County, California, USA, were used to evaluate the relationship between habitat heterogeneity, local in-stream structural features and relative sediment supply. Habitat heterogeneity was quantified using spatial heterogeneity measures from the field of landscape ecology. Relative sediment supply, as expressed by the sediment supply/transport capacity ratio, which controls channel morphology and substrate textures, two key physical habitat characteristics, was quantified using a dimensionless bedload transport ratio, q. Calculated q values were plotted against an ecologically meaningful heterogeneity index, Shannon's Diversity Index, measured for each study reach, as well as the percent area of in-stream structural elements. The results indicate two potential mechanisms for how relative sediment supply may drive geomorphic diversity in natural river systems at the reach scale. When less mobile structural elements form a small proportion of the reach landscape, the supply/capacity ratio dictates the range of sediment textures and geomorphic features observed within the reach. In these settings, channels with a moderate relative sediment supply exhibit the highest textural and geomorphic diversity. In contrast, when less mobile structural elements are abundant, forced local scour and deposition creates high habitat heterogeneity, even in the presence of high relative sediment supply.  相似文献   

Identification and definition of primary and reworked tephra in Late Glacial and Holocene marine shelf sediments off North Iceland     

Esther Ruth Gudmundsdóttir  Jón Eiríksson  Gudrún Larsen 《第四纪科学杂志》2011,26(6):589-602

Nine tephra layers in marine sediment cores (MD99‐2271 and MD99‐2275) from the North Icelandic shelf, spanning the Late Glacial and the Holocene, have been investigated to evaluate the effectiveness of methods to detect tephra layers in marine environments, to pinpoint the stratigraphic level of the time signal the tephra layers provide, and to discriminate between primary and reworked tephra layers in a marine environment. These nine tephra layers are the Borrobol‐like tephra, Vedde Ash, Askja S tephra, Saksunarvatn ash, and Hekla 5, Hekla 4, Hekla 3, Hekla 1104 and V1477 tephras. The methods used were visual inspection, magnetic susceptibility, X‐ray photography, mineralogical counts, grain size and morphological measurements, and microprobe analysis. The results demonstrate that grain size measurements and mineralogical counts are the most effective methods to detect tephra layers in this environment, revealing all nine tephra layers in question. Definition of the tephra layers revealed a 2–3 cm diffuse upper boundary in eight of the nine tephra layers and 2–3 cm diffuse lower boundary in two tephra layers. Using a multi‐parameter approach the stratigraphic position of a tephra layer was determined where the rate of change of the parameters tested was the greatest compared with background values below the tephra. The first attempt to use grain morphology to distinguish between primary and reworked tephra in a marine environment suggests that this method can be effective in verifying whether a tephra layer is primary or reworked. Morphological measurements and microprobe analyses in combination with other methods can be used to identify primary tephra layers securely. The study shows that there is a need to apply a combination of methods to detect, define (the time signal) and discriminate between primary and reworked tephra in marine environments. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Late Quaternary terrestrial tephrochronology of Iceland—frequency of explosive eruptions,type and volume of tephra deposits     

Gudrún Larsen  Jón Eiríksson 《第四纪科学杂志》2008,23(2):109-120

  相似文献   

A 3000-year varved record of glacier activity and climate change from the proglacial lake Hvítárvatn,Iceland     

Darren J. Larsen  Gifford H. Miller  Áslaug Geirsdóttir  Thorvaldur Thordarson 《Quaternary Science Reviews》2011,30(19-20):2715-2731

A suite of environmental proxies in annually laminated sediments from Hvítárvatn, a proglacial lake in the central highlands of Iceland, are used to reconstruct regional climate variability and glacial activity for the past 3000 years. Sedimentological analysis is supported by tephrostratigraphy to confirm the continuous, annual nature of the laminae, and a master varve chronology places proxies from multiple lake cores in a secure geochronology. Varve thickness is controlled by the rate of glacial erosion and efficiency of subglacial discharge from the adjacent Langjökull ice cap. The continuous presence of glacially derived clastic varves in the sediment fill confirms that the ice cap has occupied the lake catchment for the duration of the record. Varve thickness, varve thickness variance, ice-rafted debris, total organic carbon (mass flux and bulk concentration), and C:N of sedimentary organic matter, reveal a dynamic late Holocene climate with abrupt and large-scale changes in ice-cap size and landscape stability. A first-order trend toward cooler summers and ice-cap expansion is punctuated by notable periods of rapid ice cap growth and/or landscape instability at ca 1000 BC, 600 BC, 550 AD and 1250 AD. The largest perturbation began ca 1250 AD, signaling the onset of the Little Ice Age and the termination of three centuries of relative warmth during Medieval times. Consistent deposition of ice-rafted debris in Hvítárvatn is restricted to the last 250 years, demonstrating that Langjökull only advanced into Hvítárvatn during the coldest centuries of the Little Ice Age, beginning in the mid eighteenth century. This advance represents the glacial maximum for at least the last 3 ka, and likely since regional deglaciation 10 ka. The multi-centennial response of biological proxies to the Hekla 3 tephra deposition illustrates the significant impact of large explosive eruptions on local environments, and catchment sensitivity to perturbations.  相似文献   

Improving in Situ Cosmogenic Chronometers     

Douglas H. Clark  Paul R. Bierman  Patrick Larsen 《Quaternary Research》1995,44(3)

New radiocarbon ages for Sierra Nevada deglaciation, the first ¹⁰ Be measurements from the Laurentide terminal moraine, and calculations based on paleomagnetic field strength have the potential to substantially improve the accuracy of cosmogenic age estimates. Specifically, three new constraints apply to the interpretation of measured abundances of in situ produced cosmogenic ¹⁰Be and ²⁶Al: (1) A suite of minimum-limiting radiocarbon dates indicates that the Sierra Nevada was deglaciated at least several thousand years earlier than assumed when Nishiizumi et al. (1989) first calibrated ¹⁰Be and ²⁶ Al production rates based on polished bedrock surfaces in the range, with retreat beginning by 18,000 cal yr B.P. and completed by 13,000 cal yr B.P. (2) Concentrations of ¹⁰Be in moraine boulders and glacier-polished bedrock in New Jersey show little variance (10%, 1σ) and can be used to calculate a preliminary ¹⁰Be production rate (integrated over the past 21,000-22,000 cal yr B.P. at 41°, 200-300 m altitude) that is about 20% lower than currently accepted. (3) Calculations of the effect of past geomagnetic field-strength variations on production rates suggest that the use of temporally averaged production rates may generate age errors of >20%; however, cosmogenic exposure ages can be corrected for this effect, although the corrections currently are imprecise. Many previously reported late-Pleistocene ¹⁰Be and ²⁶Al exposure ages are probably too young and are less accurate and less precise than implied by reported uncertainties. The discrepancy between accepted production rates and those calculated from Laurentide exposures, when considered together with the Sierran deglacial chronology and the model results, suggest that correlations between cosmogenic and other numerical ages, especially for brief events like the Younger Dryas and Heinrich events, will not be robust until temporal variations and the altitude/latitude scaling of production rates are fully understood and quantified at levels comparable to current analytic uncertainties (3%).  相似文献